Mia Farrow, one of the Chinese government's most outspoken critics, was allowed to enter Hong Kong after a brief interview with immigration officers yesterday morning - despite the banning of other campaigners before today's Olympic torch relay.

The Hollywood actor, part of the Dream for Darfur campaign pressing China to use its leverage with Sudan to halt the bloodshed in the region, said officials had sought reassurance that the group would not disrupt the passage of the flame.

"They wanted to know what we were here for," Farrow told the Guardian. "They read us a statement about Hong Kong's position vis-a-vis the parade. We reassured them we are here to give an address and were not going near the torch.

"They were extremely gracious and their questions were reasonable." She added: "We understand the pride of Hong Kong in having the torch pass through, but it is also right to say that 2.7 million people are in camps in Darfur and eastern Chad. We want to represent them and make sure their voices can be heard."

Hong Kong, as the first location on the domestic leg of the tour, has prepared a grand send-off for the torch. But after witnessing protests along the international journey, officials were anxious to ensure a trouble-free celebration today.

Three thousand police will guard the route and authorities have deported several people attempting to enter the region - including members of the Free Tibet Campaign, human rights activists and a Chinese journalist. Dr Yu Zhang was due to chair a session at a World Press Day conference but was put on a flight back to Europe yesterday after being held at the airport for 10 hours without explanation.

The secretary-general of the Independent Chinese PEN Centre - part of the international network promoting freedom for writers - is a Chinese citizen with permanent residence in Sweden. "This is an obvious indication that the negative impact of the Beijing Olympics on Chinese citizens' rights is increasing as the games draw near, expanding beyond mainland China at least to Hong Kong," he said.

Farrow said she had been unsure whether she would be allowed into the region. "I don't know the specifics of [barred] campaigners or their intentions. If they were questioned in the way we were, I don't see why they wouldn't have been let in.

Farrow has been at the forefront of efforts to persuade China to put pressure on Sudan as an arms supplier to and major oil customer of the African state.

But Dream for Darfur also acknowledges China's role in persuading Khartoum to accept peacekeepers in the region, where the UN estimates that 200,000 have died. It says further pressure is needed because the Sudanese government is doing everything it can to prevent the full deployment mandated by the UN.

Farrow's high profile means that deporting her would inevitably have led to widespread questions about the Chinese government's handling of dissent, particularly in Hong Kong - which enjoys political freedoms not available in the mainland under the "one country, two systems" pledge. Democracy campaigners are awake to any potential erosion of civil liberties.

A column in the South China Morning Post, Hong Kong's English language newspaper, warned this week that barring Farrow would attract "international ridicule".